1. Field of the Invention
The present invention relates generally to vehicular steering systems. More particularly, the invention relates to a rack-and-pinion actuated drag link steering assembly and system.
2. Description of Related Art
Numerous strategies have been developed to actuate steering in motor vehicles. Some steering systems include a pair of steering knuckles supported on a chassis for vertical suspension purposes and for movement of wheels about a pair of axes. The wheels are rotatably mounted to the steering knuckles are free to pivot thereby allowing the vehicle to turn. A rack-and-pinion steering system typically includes a rack and pinion steering assembly fixably mounted to the chassis, and a pair of tie rods attaching the steering gear to the steering knuckles. An integral gear steering system may include a steering gear operably attached to the chassis and a drag link positioned between the steering gear and the tie rods. Both the rack-and-pinion and integral gear steering systems are usually fixably mounted to the chassis wherein no motion is provided at the fixed mount during steering maneuvers.
The integral gear steering system usually has greater mass than the rack-and-pinion steering system but relatively greater compliance due to dimensional clearances in the pivotal connections between the additional structural elements. The integral gear steering system may be more suitable for motor “heavy-use” vehicles subject to a wide range of loads (e.g., vans, trucks, sport utility vehicles, etc.) than the rack-and-pinion steering system unless complex and expensive structure is provided to account for the reduced compliance of the rack-and-pinion steering system relative to the integral gear steering system. The rack-and-pinion type steering system, however, may be advantageous to other types of steering arrangements (including integral gear steer systems) in that it is relatively lightweight, has a comparatively simple arrangement, provides superior steering performance, and requires a small mounting space.
FIG. 1 is a perspective view of a prior art rack-and-pinion assembly, shown generally by numeral 10. Assembly 10 comprises a cylindrical housing 20 including a slidable rack 22 partially enclosed therein. Rack 22 includes a plurality of teeth 24 that engage complementary teeth 26 on a pinion gear 28. Tie rods 30, 32 are positioned at opposing ends of the rack 22 for attachment to steering knuckles (not shown). A plurality of chassis mounts 34, 36 provide fixable attachment means to a vehicle chassis. Pinion gear 28 may be coupled to a steering wheel (not shown) and a shaft 38 so that when a vehicle operator turns the steering wheel, pinion gear teeth 26 rotatably mesh with corresponding rack teeth 24. The rotational movement of the steering wheel is converted into a linear motion on the rack 22 thereby providing the motion to turn the vehicle wheels. Typically, a gear reduction between the pinion gear 28 and rack 22 is provided to make it easier for the vehicle operator to steer.
Many rack-and-pinion type steering designs include means for hydraulically assisting the motion of the rack-and-pinion and, thus, the steering wheel. In this case, a piston 40 is slidably positioned within a fluid chamber 42 of the housing 20 whereby hydraulic fluid 44 pressure may build-up on either side of the piston 40 during steering maneuvers. The pressure difference forces the piston 40 to translate in a direction according to the rotation of a steering wheel thereby providing an assisting force to a vehicle operator. Hydraulic ports 46, 48 allow differential fluid flow on either side of the piston 40. To control the hydraulic fluid 44 pressures, a rotary valve 50 may be provided to sense force applied to the steering wheel. The rotary valve 50 controls a hydraulic pump (not shown), which can generate the differential fluid pressure on the piston 40 through a hydraulic circuit 52, which includes the hydraulic ports 46, 48.
The integral gear steer system may include a recirculating ball steering gear and linkage. The gear may contain a worm gear including a threaded shaft positioned within a correspondingly threaded block. The block is fixed to the shaft (and the steering wheel), so the steering wheel, shaft, and block may turn in unison. The worm gear may include a plurality of ball bearings positioned within threads of the shaft and block to reduce friction, wear, and steering tolerance or so-called “slop”. The block may include additional teeth that engage a sector gear or like member attached to a cross link steering system.
FIG. 2A is an elevated perspective view of a prior art integral gear steering system 70 operably attached to first and second vehicle wheels 80, 82 wherein the steering system 70 is shown in a “straight” configuration. Steering system 70 includes a swinging pitman arm 72 that pivots with respect to a vehicle chassis 84 at a pivoting link 74. Pitman arm 72 is connected to a recirculating ball steering gear, which is connected to an intermediate shaft and a steering column (note: gear, shaft, and column are not shown). A drag link bar 76 is operably attached to the pitman arm 72 and the first vehicle wheel 82 through a steering knuckle (not visible). Drag link bar 76 typically incorporates an adjustment sleeve for steering wheel centering. A cross car link bar 78 is operably attached to both wheels 80, 82 and an anti-sway bar 86 is operably attached adjacent to the cross car link bar 78 ends.
FIG. 2B is an elevated perspective view of the integral gear steering system 70 wherein the steering system 70 is shown in a “right turn” configuration. During operation of the steering system 70, rotation (i.e., in a clockwise direction from the vehicle operator's perspective) of the steering wheel, column, shaft, and gear cause a swinging movement of pitman arm 72. The pitman arm 72 motion biases the drag link bar 76 toward the first vehicle wheel 82 thereby making it pivot to the “right”. The first vehicle wheel 82 cooperates with the cross car link bar 78 to simultaneously turn the second wheel 82 to the “right”. As with the rack-and-pinion steering assembly, turn assist may be provided by a high-pressure hydraulic system (not shown) wherein fluid pressure provides rotational force to the steering block.
Although the rack-and-pinion and integral gear steering systems may provide adequate steering in many vehicle applications, numerous changes may be implemented to improve these systems. For example, it would be desirable to provide a rack-and-pinion type steering system that is simpler in design and includes less moving parts than an integral gear steer system but may be readily adapted for use in “heavy-use” vehicles.
Therefore, it would be desirable to provide a rack-and-pinion type steering device and assembly that overcomes the aforementioned and other disadvantages.